The present invention relates to an indirect ophthalmoscopy contact lens system for observing and treating the retina of a patient's eye, and more particularly to an indirect ophthalmoscopy contact lens system which produces an erect, real, aerial image of the retina which can be viewed through a microscope for diagnostic, therapeutic and surgical purposes.
My prior U.S. Pat. No. 5,200,773 discloses an ophthalmoscopy contact lens system of this type which comprises a unitary device that is placed on a patient's eye for producing the erect, aerial image of the retina. This device includes a holder in which there is mounted a meniscus contact lens element having a concave posterior surface for placement on the cornea and an image forming lens mounted anterior to the contact lens element which collects light emanating from the retina and passing through the contact lens element to produce an inverted, real, aerial image of the retina anterior to the imaging forming lens. An erecting optical system is located inside the holder which reinverts the inverted image produced by the image forming lens to produce an erect, real, retinal image that can be viewed through a microscope, such as a slit lamp biomicroscope or operating microscope. The erecting system within the holder is disclosed in my prior patent as comprising a prism structure, such as a Pechan prism, or alternatively coaxial lenses anterior of the image forming lens which have refractive powers to enable a re-inversion of the inverted, aerial image.
One criteria of a unitary device such as that disclosed in my above mentioned patent is that the device have a relatively short length from the posterior surface of the contact lens element to the most anterior optical surface of the device so that the device can be positioned in a stable and comfortable manner on the patient's eye. If the device is too long, it can produce undesirable stresses on the patient's eye and is more subject to being inadvertently touched by the physician, for example, when maneuvering the microscope or surgical instrumentation. Through experimentation and development, I have found that a desirable length for the unitary device is less that 40 mm, and preferably closer to 30 mm. A unitary device containing a prism structure was made that met this length criteria. However, I have found that the prism structure renders a device that is too bulky in its width dimension and too heavy to be of practical use. Additionally the prism structure may limit the binocular field of view.
Non-contact, indirect ophthalmoscopy systems that produce an erect image are known which avoid the length criteria since, by design and use, they do not touch the eye. For example, David Volk discloses in his U.S. Pat. No. 4,721,378 a handheld, indirect ophthalmoscopy lens device of the non-contact type which produces an erect, aerial image of the retina that can be viewed through a microscope. The David Volk device includes three biconvex lenses mounted in a holder. In use, the lens that is closest to the patient's eye forms a real, inverted aerial image of the retina that is reinverted by the optics of the following two lenses. One difficulty associated with the use of this device is maintenance of optical alignment and positioning between the patient's eye and the viewing device such that the retinal image view is not diminished or lost during observation. Another drawback is that this non-contact device cannot achieve as large a field of view as a contact, indirect ophthalmoscopy lens.
U.S. Pat. No. 5,282,085 discloses a stereoscopic microscope in which a non-contact image forming lens together with inversion optics are provided as a removable attachment to the microscope. In the embodiment disclosed in FIG. 3 of this patent, the attachment comprises a three lens system similar to that of the above mentioned David Volk patent. A so-called field magnifying lens forms an inverted, aerial image of the patient's retina that is re-inverted by the following two lenses. In other embodiments of U.S. Pat. No. 5,282,085, the re-inversion is performed by a single lens or by a prism arrangement anterior of the field magnifying lens. In any case, the alignment between the inversion optics attachment, which includes the first image forming lens (i.e. the field magnifying lens), is fixed relative to the optical axis of the microscope. Although U.S. Pat. No. 5,282,085 offers some advantages with respect to the non-contact type ophthalmoscopy lens system with re-inversion optics, it still suffers from the fact that movement of the microscope together with the attachment relative to the patient's eye can easily result in diminution or loss of the fundus image, and the field of view is still limited relative to that of a contact indirect ophthalmoscopy lens system. Another disadvantage of this system relates to the proximity of the non-contact image forming lens to the patient's cornea which with a short focal length lens may be problematic.